1. Field of the Invention
The present invention relates to the field of pharmaceutical preparations and provides new retard preparations containing pinacidil (N"-cyano-N-4-pyridyl-N'-1,2,2-trimethylpropylguanidine).
2. Description of the Prior Art
In order to continuously maintain the effect of a certain drug, various methods have been attempted which can be classified into the following two categories:
(a) Single phase structure which slowly releases the active ingredient (i.e. prolonged-release type); PA1 (b) Two phase preparations in which one of the two phases is a rapid-release type and the other a sustained-release type (i.e. sustained-release type).
The present preparations are classified into the (b) type. In order to manufacture a retard preparation from a plain drug, it is necessary to clarify the biological or pharmaceutical characteristics as well as physicochemical properties of the drug. Then, the method applicable to the drug is usually selected from a variety of techniques for pharmaceutical preparations according to the above clarified properties.
N-Keflex.RTM., an antibiotic oral-preparation of sustained-release type, consists of two components, i.e. plain granules (rapid-release one) and enteric granules (delayed-release one). In this preparation, the enteric coating granules prolong the absorption of drug in the intestine to give a long-acting effect to the preparation [described in U.S. Pat. No. 4250166, (Jap. Pat. Pub. No. 55-47611)].
In another case, a long-acting granular preparation of the single phase structure containing theophylline, which is used for treating a pulmonary disease, has been described in Japanese Patent Publication No. 55-153715. The preparation of theophylline is a prolonged-release type which contains theophylline as the active ingredient, a metal salt of higher fatty acid and ethylcellulose in a certain amount, from which the active ingredient is released moderately.